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          <div>
            <h2 class="title"><a id="wrapup"></a>Chapter 6. Summary and Examples</h2>
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      <div class="toc">
        <p>
          <b>Table of Contents</b>
        </p>
        <dl>
          <dt>
            <span class="sect1">
              <a href="wrapup.html#anatomy">Anatomy of a Transactional Application</a>
            </span>
          </dt>
          <dt>
            <span class="sect1">
              <a href="txnexample_c.html">Transaction Example</a>
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          <dt>
            <span class="sect1">
              <a href="inmem_txnexample_c.html">In-Memory Transaction Example</a>
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      <p>
        Throughout this manual we have presented the concepts and
        mechanisms that you need to provide transactional protection for
        your application. In this chapter, we summarize these
        mechanisms, and we provide a complete example of a multi-threaded
        transactional DB application.
  </p>
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            <div>
              <h2 class="title" style="clear: both"><a id="anatomy"></a>Anatomy of a Transactional Application</h2>
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        <p>
        Transactional applications are characterized by performing the
        following activities:
    </p>
        <div class="orderedlist">
          <ol type="1">
            <li>
              <p>
                Create your environment handle.
            </p>
            </li>
            <li>
              <p>
                Open your environment, specifying that the following
                subsystems be used:
            </p>
              <div class="itemizedlist">
                <ul type="disc">
                  <li>
                    <p>
                        Transactional Subsystem (this also initializes the
                        logging subsystem).
                    </p>
                  </li>
                  <li>
                    <p>
                        Memory pool (the in-memory cache).
                    </p>
                  </li>
                  <li>
                    <p>
                        Logging subsystem.
                    </p>
                  </li>
                  <li>
                    <p>
                        Locking subsystem (if your application is multi-process or multi-threaded).
                    </p>
                  </li>
                </ul>
              </div>
              <p>
                It is also highly recommended that you run normal recovery 
                upon first environment open. Normal recovery examines only those logs required
                to ensure your database files are consistent relative to the information found in your
                log files.
            </p>
            </li>
            <li>
              <p>
                Optionally spawn off any utility threads that you might need. Utility
                threads can be used to run checkpoints periodically, or to
                periodically run a deadlock detector if you do not want to
                use DB's built-in deadlock detector.
            </p>
            </li>
            <li>
              <p>
                Open whatever database handles that you need.
            </p>
            </li>
            <li>
              <p>
                Spawn off worker threads. How many of these you need and
                how they split their DB workload is entirely up to your
                application's requirements. However, any worker threads
                that perform write operations will do the following:
            </p>
              <div class="orderedlist">
                <ol type="a">
                  <li>
                    <p>
                        Begin a transaction.
                    </p>
                  </li>
                  <li>
                    <p>
                        Perform one or more read and write
                        operations.
                    </p>
                  </li>
                  <li>
                    <p>
                        Commit the transaction if all goes well.
                    </p>
                  </li>
                  <li>
                    <p>
                        Abort and retry the operation if a deadlock is
                        detected.
                    </p>
                  </li>
                  <li>
                    <p>
                        Abort the transaction for most other errors.
                    </p>
                  </li>
                </ol>
              </div>
            </li>
            <li>
              <p>
                On application shutdown:
            </p>
              <div class="orderedlist">
                <ol type="a">
                  <li>
                    <p>
                        Make sure there are no opened cursors.
                    </p>
                  </li>
                  <li>
                    <p>
                        Make sure there are no active transactions. Either
                        abort or commit all transactions before shutting
                        down.
                    </p>
                  </li>
                  <li>
                    <p>
                            Close your databases.
                    </p>
                  </li>
                  <li>
                    <p>
                        Close your environment.
                    </p>
                  </li>
                </ol>
              </div>
            </li>
          </ol>
        </div>
        <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
          <h3 class="title">Note</h3>
          <p>
                Robust DB applications should monitor their worker threads to
            make sure they have not died unexpectedly. If a thread does
            terminate abnormally, you must shutdown all your worker threads
            and then run normal recovery (you will have to reopen your
            environment to do this). This is the only way to clear any
            resources (such as a lock or a mutex) that the abnormally
            exiting worker thread might have been holding at the time that
            it died.
        </p>
          <p>
            Failure to perform this recovery can cause your
            still-functioning worker threads to eventually block forever
            while waiting for a lock that will never be released.
        </p>
        </div>
        <p>
        In addition to these activities, which are all entirely handled by
        code within your application, there are some administrative
        activities that you should perform:
    </p>
        <div class="itemizedlist">
          <ul type="disc">
            <li>
              <p>
                Periodically checkpoint your application. Checkpoints will
                reduce the time to run recovery in the event that one is
                required. See <a class="xref" href="filemanagement.html#checkpoints" title="Checkpoints">Checkpoints</a>
                for details.
            </p>
            </li>
            <li>
              <p>
                Periodically back up your database and log files. This is
                required in order to fully obtain the durability guarantee
                made by DB's transaction ACID support. See
                <a class="xref" href="backuprestore.html" title="Backup Procedures">Backup Procedures</a>
                for more information.
            </p>
            </li>
            <li>
              <p>
                You may want to maintain a hot failover if 24x7 processing
                with rapid restart in the face of a disk hit is important
                to you. See <a class="xref" href="hotfailover.html" title="Using Hot Failovers">Using Hot Failovers</a>
                for more information.
            </p>
            </li>
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